Meteorological mechanisms of regional PM2.5 and O3 transport in the North China Plain driven by the East Asian monsoon

Abstract

The regional transport of air pollutants significantly affects downwind air quality in the North China Plain (NCP), which forms part of the East Asian monsoon region. Here, we investigated the meteorological regional transport mechanisms that lead to wintertime PM2.5 and summertime O3 pollution episodes in downwind regions over the NCP during the East Asian monsoon. First, we analyzed the spatiotemporal patterns of PM2.5 and O3 pollution during the summers and winters of 2015–2020 in the NCP, as well as the influence of meteorological conditions. Subsequently, we identified the typical regional transport patterns of wintertime PM2.5 and summertime O3 using the multivariable empirical orthogonal function with multi-source data. The results showed that prevailing southerly and southeasterly winds in summer aggravated PM2.5 and O3 pollution over the northern NCP. Conversely, prevailing northerly and northwesterly winds in winter exacerbated PM2.5 and O3 pollution over the southern NCP. Wintertime PM2.5 pollution events in Henan (on the southern edge of the NCP) were induced by the southward movement of weak cold airflow following northerly winds governed by the East Asian winter monsoon. Additionally, a warm air mass to the south of Henan and the high surrounding terrain inhibited further southward invasion of weak cold air, causing heavy PM2.5 pollution. Conversely, summertime O3 pollution episodes in Beijing (on the northern edge of the NCP) were associated with southerly and southeasterly winds, which drove the transport of O3 and its precursors from the southern NCP to Beijing. The mountain barrier in northern Beijing aggravated O3 pollution. During the O3 pollution events, Beijing was in a transitional regime, and HCHO and NO2 increased by 17.16% and 20.43%, respectively. Furthermore, the vertical structure of the atmosphere facilitated the downward mixing of PM2.5 and O3 transported during pollution episodes. These results provide a theoretical reference for predicting and controlling heavy air pollution in the NCP.